1,564 research outputs found
Dynamical GUT breaking and mu-term driven supersymmetry breaking
Models for dynamical breaking of supersymmetric grand unified theories are
presented. The doublet-triplet splitting problem is absent since the Higgs
doublet superfields can be identified with the massless mesons of the strong
gauge group whereas there are no massless states corresponding to the colored
Higgs fields. Various strong gauge groups SU(Nc), Sp(Nc) and SO(Nc) are
examined. In a model with SO(9) strong gauge group, adding the mu-term for the
Higgs fields triggers to break supersymmetry in a meta-stable vacuum. The
pattern of the supersymmetry breaking parameters is predicted to be the
gauge-mediation type with modifications in the Higgs sector.Comment: 23 pages, 1 figure; version to appear in PR
Comments on Diquarks, Strong Binding and a Large Hidden QCD Scale
We present arguments regarding diquarks possible role in low-energy hadron
phenomenology that escaped theorists' attention so far. Good diquarks, i.e. the
states of two quarks, are argued to have a two-component structure with
one of the components peaking at distances several times shorter than a typical
hadron size (a short-range core). This can play a role in solving two old
puzzles of the 't Hooft 1/N expansion: strong quark mass dependence of the
vacuum energy density and strong violations of the Okubo-Zweig-Iizuka (OZI)
rule in the quark-antiquark channels. In both cases empiric data defy
't Hooft's 1/N suppression. If good diquarks play a role at an intermediate
energy scale they ruin 't Hoofts planarity because of their mixed-flavor
composition. This new scale associated with the good diquarks may be related to
a numerically large scale discovered in [V. Novikov, M. Shifman, A. Vainshtein
and V. Zakharov, Nucl. Phys. B 191, 301 (1981)] in a number of phenomena mostly
related to vacuum quantum numbers and glueball channels. If SU(3) of bona fide QCD is replaced by SU(2), diquarks become
well-defined gauge invariant objects. Moreover, there is an exact symmetry
relating them to pions. In this limit predictions regarding good diquarks are
iron-clad. If passage from SU(2) to SU(3) does not
lead to dramatic disturbances, these predictions remain qualitatively valid in
bona fide QCD.Comment: 18 pages, 3 figures; journal version, minor change
Mass Spectrum in SQCD and Problems with the Seiberg Duality. Another Scenario
N=1 SQCD with SU(N_c) colors and N_F flavors of light quarks is considered
within the dynamical scenario which assumes that quarks can be in two different
phases only. These are: a) either the HQ (heavy quark) phase where they are
confined, b) or they are higgsed, at the appropriate values of parameters of
the Lagrangian.
The mass spectra of this (direct) theory and its Seiberg's dual are obtained
and compared, for quarks of equal or unequal masses. It is shown that in all
cases when there is the additional small parameter at hand (it is
0<(3N_c-N_F)/N_F << 1 for the direct theory, or its analog 0<(2N_F-3N_c)/N_F <<
1 for the dual one), the mass spectra of the direct and dual theories are
parametrically different. A number of other regimes are also considered.Comment: 30 pages, purely technical improvements for readers convenienc
Semileptonic Decays of Heavy Lambda Baryons in a Quark Model
The semileptonic decays of Lambda_c and Lambda_b are treated in the framework
of a constituent quark model. Both nonrelativistic and semirelativistic
Hamiltonians are used to obtain the baryon wave functions from a fit to the
spectra, and the wave functions are expanded in both the harmonic oscillator
and Sturmian bases. The latter basis leads to form factors in which the
kinematic dependence on q^2 is in the form of multipoles, and the resulting
form factors fall faster as a function of q^2 in the available kinematic
ranges. As a result, decay rates obtained in the two models using the Sturmian
basis are significantly smaller than those obtained using the harmonic
oscillator basis. In the case of the Lambda_c, decay rates calculated using the
Sturmian basis are closer to the experimentally reported rates. However, we
find a semileptonic branching fraction for the Lambda_c to decay to excited
Lambda* states of 11% to 19%, in contradiction with what is assumed in
available experimental analyses. Our prediction for the Lambda_b semileptonic
decays is that decays to the ground state Lambda_c provide a little less than
70% of the total semileptonic decay rate. For the decays Lambda_b to Lambda_c,
the analytic form factors we obtain satisfy the relations expected from
heavy-quark effective theory at the non-recoil point, at leading and
next-to-leading orders in the heavy-quark expansion. In addition, some features
of the heavy-quark limit are shown to naturally persist as the mass of the
heavy quark in the daughter baryon is decreased.Comment: 51 pages, 8 figures, submitted to Physical Review
Structure of the and the strong coupling constant with the light-cone QCD sum rules
In this article, we take the point of view that the charmed scalar meson
is the conventional meson and calculate the strong
coupling constant within the framework of the light-cone QCD
sum rules approach. The numerical values for the large scalar- coupling
constant support the hadronic dressing mechanism. Just like
the scalar mesons and , the may have small
scalar kernel of the typical meson size. The strong
coupling to the hadronic channels (or the virtual mesons loops) may result in
smaller mass than the conventional scalar meson in the constituent
quark models, and enrich the pure state with other components. The
may spend part (or most part) of its lifetime as virtual
state.Comment: 17 pages, 7 figure, revised version, add detailed error analysi
Radiative corrections to electroweak parameters in the Higgs triplet model and implication with the recent Higgs boson searches
We study radiative corrections to the electroweak parameters in the Higgs
model with the Y=1 triplet field, which is introduced in the scenario of
generating neutrino masses based on the so-called type II seesaw mechanism. In
this model, the rho parameter deviates from unity at the tree level.
Consequently, the electroweak sector of the model is described by the four
input parameters such as , , and
. We calculate the one loop contribution to the W boson mass as
well as to the rho parameter in order to clarify the possible mass spectrum of
the extra Higgs bosons under the constraint from the electroweak precision
data. We find that the hierarchical mass spectrum among ,
and (or ) is favored by the precision data especially for the case of
, where , , and
are the doubly-charged, singly-charged, CP-odd and CP-even Higgs bosons
mainly originated from the triplet field. We also discuss phenomenological
consequences of such a mass spectrum with relatively large mass splitting. The
decay rate of the Higgs boson decay into two photons is evaluated under the
constraint from the electroweak precision data, regarding the recent Higgs
boson searches at the CERN LHC.Comment: 17 pages, 23 figures, version published in PRD, title slightly
modifie
On the Significance of the Quantity "A Squared"
We consider the gauge potential A and argue that the minimum value of the
volume integral of A squared (in Euclidean space) may have physical meaning,
particularly in connection with the existence of topological structures. A
lattice simulation comparing compact and non-compact ``photodynamics'' shows a
jump in this quantity at the phase transition, supporting this idea.Comment: 6 pages, one figur
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